Estimation of Radiation Doses in a Case-control Study of Thyroid Cancer in French Polynesia

Abstract

P-593 Introduction: A case-control study of thyroid cancer was carried out in French Polynesia. The study includes close to 600 subjects both cases and controls all aged up to 36 years old at the time of atmospheric nuclear weapons tests that were conducted between 1966 and 1974 in French Polynesia. Methods: Radiation doses to the thyroids of the subjects were assessed based on the available historical results of radiometric measurements and meteorological data. These included annual reports on the radiological situation in French Polynesia that had been sent to the Secretariat of UNSCEAR. Results of measurements of exposure rate and of total activity in filtered air were used to evaluate the ground depositions of specific radionuclides. Radiation monitoring also included measurements of 131I and 137Cs in cow's milk produced in Tahiti and measurements of radioactivity in foodstuffs produced on the selected islands. Results: For each atmospheric nuclear weapons test that contributed substantially to the local deposition of radionuclides, the radiation dose to the thyroid from 131I intake via inhalation and ingestion was estimated. In additional, thyroid doses from the intake of short-lived radioiodines and 132Te, external exposure from radionuclides deposited on the ground, and ingestion of long-lived 137Cs were reconstructed. The assessment of individual thyroid doses took into account the residential history and dietary habits of the subjects, which was obtained during the personal interview. Discussion and Conclusions: Intake of 131I with locally produced foodstuffs (cows’ milk on Tahiti, leafy vegetables) was the dominant pathways of thyroid exposure for the majority of the study subjects. Drinking of rainwater was also important pathway of exposure to persons who resided in Tuamotu Archipelago. The dose estimates that have been obtained are based on a rather limited number of radiological measurements performed on a limited number of islands. Therefore, the reconstructed doses associated with high uncertainties arising from (1) the procedures of interpolation and extrapolation used to reconstruct the environmental radiation field in locations without measurements, (2) the assumptions made, and (3) uncertainties in dosimetric models. A thorough compilation of the results of all radiological monitoring that was carried out in French Polynesia in 1966–1974 would greatly improve the reliability and the precision of the dose estimates. This work was supported by Association pour la Recherche sur le Cancer, Direction Générale de la Santé, Conseil de Radioprotection d'Electricité de France, Agence Française de Sécurité Sanitaire et Environnementale, and CHILD-THYR project of the EC.